Study On Bearing Mechanism And Design Method Of Repairing Rusty K-joints With GFRP Interlayer Grouting

Hollow steel pipe structure is widely used in Chinese buildings,long-span Bridges and offshore platforms.However,steel pipe,as a kind of metal material,will inevitably appear corrosion after a long time of service,and the mechanical properties of the material will be reduced,which has a serious impact on the normal use and safety performance of the structure.In addition,the stress distribution in the node region is more complex than that in other regions.The coating near the node is prone to spalling,and the weld seam in the node region is prone to cracks and other phenomena.If the node is in a corroded state,it is easy to cause serious safety accidents,so it is necessary to study the repair of the existing steel structure node after corrosion.It is urgent to propose an effective repair method.In this study,K-shaped joints of circular steel tubes,which are widely used in steel pipe structure,are selected to solve the problem of decreasing bearing capacity after joint corrosion,and the proposed GFRP interlayer grouting method is adopted to repair the rusty K-shaped joints.Through finite element simulation and theoretical analysis,the failure mode and bearing capacity of the repaired node were studied deeply,and the bearing mechanism of the repaired node was defined.The design method and construction suggestions for the repaired joints are put forward,which is of significant importance to the bearing capacity and safety performance of the corroded hollow steel pipe structure,and can effectively solve the application problems in practical engineering.Then ANSYS software is used for finite element simulation,and the concrete steps of simulation modeling are introduced in detail,including element selection,mesh division,material constitutive,interaction and boundary conditions,etc.Through the comparison of failure mode and load displacement curve,it is verified that the finite element simulation scheme used in this thesis has good accuracy,which lays a foundation for the following analysis of bearing performance parameters of the damaged K-shaped joints repaired by GFRP interlayer grouting.Further parameter analysis of K-shaped joints repaired by GFRP interlayer grouting shows that the main diameter ratio and main corrosion rate are the key factors affecting the unrepaired and GFRP interlayer grouting repairing K-shaped joints.For the tensile capacity of joints,if the main diameter ratio is relatively small,the joint bearing capacity increases more.For the bearing capacity of joints,the bearing capacity of joints increases more when the diameter ratio of branches is relatively large.Increasing the thickness of GFRP tube and grout sandwich can significantly improve the tensile and compression capacity of joints.Taking the node β of 0.4 as an example,when the corrosion rate of the unrepaired node is 20%,the tensile capacity of the repaired node increases by 32%,15% higher than that of the uncorroded node.Taking the node with beta of 0.8 as an example,the maximum compressive capacity of the repaired node is increased by 37%,and that of the node without corrosion is increased by 18%.In addition,the length of GFRP coating and the strength parameters of grouting material have little influence on the bearing performance of the joints.For the repair joints with different angles,the ultimate bearing capacity in tension and compression increased significantly.Then,according to the parameter analysis results obtained by finite element simulation,the bearing mechanism of K-shaped joints of ordinary round steel pipes and K-shaped joints repaired by GFRP interlayer grouting under the action of branch pipe axial force was analyzed in detail in this thesis.Combined with the key parameters affecting the bearing performance of repaired joints,The construction suggestions of GFRP interlayer grouting joints under various geometric parameters are put forward.In this thesis,based on the existing standard formula,Origin nonlinear fitting method is used to propose a bearing capacity design formula for repairing rusty K-shaped joints with GFRP interlayer grouting,and the calculation results are compared with the results of parameter analysis.In addition,the accuracy of the formula was verified by L16-4-4 four-parameter and four-level orthogonal analysis method,and the applicability of the formula obtained by this method was extended and improved.Finally,five round steel tube truss models are established,which are not reinforced or reinforced by GFRP interlayer grouting.The bearing capacity of the joints is an important factor of the overall bearing capacity of the truss structure.The use of GFRP interlayer grouting can effectively improve the overall bearing capacity of the truss structure,and the bearing capacity can be increased by up to 36.3% compared with that of the unreinforced truss.And the failure mode of the truss structure itself and its joints is changed.After the truss structure is reinforced by GFRP interlayer grouting,the vertical deformation value at the mid-span position and the four-point point decreases obviously,and the slope of the deflection curve from the four-point point to the midspan decreases obviously,which improves the overall mechanical performance of the structure and makes the overall deformation of the truss more uniform,the suggestions of truss reinforcement are given.There are 38 figures,8 tables and 93 references in this thesis.